Wafer holder for semiconductor manufacturing device and semiconductor manufacturing device equipped with the same

ABSTRACT

A wafer holder uniformly heats a wafer at high temperatures without being damaged. A semiconductor manufacturing apparatus is provided with this wafer holder. The contact surface area where the wafer and the wafer mounting surface of the wafer-holding part are in contact includes a contact surface area A in an outer circumferential area that is farther than 1/√2R from the center of the wafer, where R is the radius of the wafer, and a contact surface area B in an inner circumferential area that is within 1/√2R of the center. The contact surface area is established so that A&gt;B. In order to obtain this relationship, the wafer-contacting part of the wafer mounting surface is preferably formed into annular convexities or embossed convexities.

FIELD OF THE INVENTION

The present invention relates to a wafer holder that is used for heating wafers during the process of semiconductor manufacturing and to a semiconductor manufacturing apparatus that is provided with the wafer holder. The present invention particularly relates to a wafer holder that is used for heating when forming films, performing etching, applying resists, or carrying out other actions on a wafer using CVD or the like and to a semiconductor manufacturing apparatus that is provided with the wafer holder.

BACKGROUND OF THE INVENTION

A variety of wafer holders have been conventionally used in order to mount wafers and perform heat treatments during semiconductor manufacturing processes. For example, a wafer holder joined to a convex support member for mounting a wafer is disclosed in Japanese Laid-Open Patent Application Publication No. 4-78138. Japanese Laid-Open Patent Application Publication No. 6-252055 describes a way of reducing the stress on a ceramic heater, which is used for raising the temperature, by increasing the temperature distribution of the ceramic heater in the vicinity of the central part. High temperature treatments have been especially needed over the past several years in order to improve throughput when forming films using CVD or the like.

SUMMARY OF THE INVENTION

Problems the Invention is Intended to Solve

The temperature of the wafer must usually be uniform when performing heat treatments in order ensure that conditions for film formation and the like are uniform. It shall be apparent, however, that large amounts of heat escape from the outer circumferential part of the wafer holder when the temperature of the wafer is high, and therefore the temperature in the vicinity of the central part of the wafer holder must set lower than in the outer circumferential part. However, if the temperature in the central part of the wafer holder is made relatively low, as described in the aforementioned Japanese Laid-open Patent Application Publication No. 6-252055, the stress acting on the wafer holder increases, possibly resulting in damage to the wafer holder and other problems.

In light of such problems with the conventional art, it is an object of the present invention to be able to heat wafers uniformly at high temperatures and to provide a wafer holder that will not be damaged under such conditions and a semiconductor manufacturing apparatus that is provided with this wafer holder.

Means Used to Solve the Above Mentioned Problems

In order to solve the above-mentioned problems, the inventors of the present invention investigated relieving the stress acting on the wafer holder by making use of the shape of the wafer mounting surface. As a result, it was discovered that stress acting on the wafer holder can be relieved, damage can be prevented, and the wafer can be uniformly heated by controlling the amount of heat that is conveyed to the wafer from the wafer mounting surface, or, more specifically, by increasing the amount of heat conveyed to the wafer from the outer circumferential area of the wafer mounting surface and reducing the amount of heat conveyed from the inner circumferential area near the center.

Specifically, the wafer holder for a semiconductor manufacturing apparatus provided by the inventors of the present invention is a wafer holder for a semiconductor manufacturing apparatus comprising a resistance heater, wherein the surface area of contact between a wafer and the wafer mounting surface of a wafer-holding part satisfies the relation A>B, where A is the contact surface area in an outer circumferential area that is farther than 1/√2R from the center of the wafer, R is the radius of the wafer, and B is the contact surface area in an inner circumferential area that is within 1/√2R of the center.

In the wafer holder for a semiconductor manufacturing apparatus of the present invention, A>2B is preferable for the contact surface area between the wafer mounting surface and the wafer, and B=0 is especially preferable for the contact surface area between the wafer mounting surface and the wafer.

A wafer-contacting part of the wafer mounting surface of the wafer holder for a semiconductor manufacturing apparatus of the present invention is preferably an annular convexity or an embossed convexity.

The wafer holder for a semiconductor manufacturing apparatus of the present invention comprises a support member for supporting the wafer-holding part, wherein the support member is physically anchored or chemically joined to the wafer-holding part.

The present invention also provides a semiconductor manufacturing apparatus comprising the wafer holder for a semiconductor manufacturing apparatus of the present invention.

Effect of the Invention

According to the present invention, the contact surface area where the wafer mounting surface and the wafer are in contact is optimized in the outer circumferential area and the inner circumferential area of the wafer, whereby a wafer holder can be provided that has excellent heating uniformity and does not suffer damage when the wafer is heated at high temperatures, even without the temperature distributions in both regions being changed.

DETAILED DESCRIPTION OF THE INVENTION

The contact surface area where a wafer mounting surface of a wafer holder of the present invention contacts a wafer is made so that the shape of the wafer-contacting part of the wafer mounting surface is changed between an outer circumferential side and an inner circumferential side, whereby the contact surface area in the outer circumferential area of the wafer is made to be larger than the contact surface area in the inner circumferential area. Specifically, the outer circumferential area is the portion farther than 1/√2R from the center of the wafer, where R is the radius of the wafer, and the inner circumferential area is the portion that is within 1/√2R from the center (in other words, the outer circumferential area and the inner circumferential area are on the same surface). When the contact surface area in the outer circumferential area is A, and the contact surface area in the inner circumferential area is B, the contact surface area between the wafer mounting surface and the wafer is established so that A>B. Heating uniformity can thereby be attained in the wafer itself while damage to the wafer holder during heating can be prevented.

The wafer mounting surface that holds the wafer in conventional wafer holders is usually a flat surface or has, e.g., round protruding parts called embossments formed over the entire wafer mounting surface. The area of the wafer and the contact surface area where the wafer contacts the wafer mounting surface are the same when such a wafer mounting surface is, e.g., flat. Even when embossments are formed, the embossments are formed uniformly over the entire wafer mounting surface of the wafer holder, and therefore the area of the wafer and the contact surface area where the wafer contacts the wafer mounting surface are the same.

The effects of the temperature of the wafer holder are directly reflected in the wafer in conventional wafer mounting surfaces having these shapes. During heat treatments, which include periods of raising and lowering temperature, the amount of heat escaping from the outer edges increases at high temperatures and temperature uniformity is compromised in the wafer holder and in the wafer, and therefore the temperature of the wafer holder must be controlled so that the temperature in the outer circumferential part is higher than in the inner circumferential part. When the temperature of the outer circumferential part is controlled so as to be higher than the inner circumferential part as in the aforementioned Japanese Laid-open Patent Application Publication No. 6-252055, however, the stress acting on the wafer holder increases and, in the worst case, the wafer holder suffers damage.

Alternatively, the contact surface area between the wafer mounting surface and the wafer in the wafer holder of the present invention is established so that the outer circumferential area of the wafer is larger than the inner circumferential area, as described above, and therefore more heat can be conveyed to the wafer through the outer circumferential area than through the inner circumferential area.

The temperature of the wafer can therefore be made uniform without increasing the temperature of the outer circumferential part of the wafer holder, from which heat easily escapes. In other words, since the contact surface area is larger in the outer circumferential area, the amount of heat conveyed to wafer from the outer circumferential area increases, and, provided that the temperature of the wafer holder is uniform, the temperature of the outer circumferential area of the wafer will rise correspondingly.

Since heat easily escapes from the outer edges of the wafer holder, the temperature of the inner circumferential area of the wafer holder actually becomes larger than in the outer circumferential area, and therefore the wafer can be heated uniformly and the stress acting on the wafer holder can be minimized. Excellent heating uniformity can therefore be obtained and damage to the wafer holder due to stress can be prevented in the wafer holder of the present invention without establishing the temperature of the outer circumferential area to be higher than the temperature of the inner circumferential area. In order to achieve even better heating uniformity, however, a resistance heater of the wafer holder is made into a two-zone heater, allowing the temperature of the outer circumferential area and the temperature of the inner circumferential area to be controlled separately.

When the contact surface area in the outer circumferential area is A, and the contact surface area in the inner circumferential area is B, it is necessary that A>B, as above, but A≧2B is preferable. The amount of heat conveyed from the outer circumferential area is increased by using such a ratio of contact surface areas, and therefore better heating uniformity can be achieved even if the temperature in the vicinity of the central part of the wafer holder becomes relatively high. Making B=0, in particular, results in better heating uniformity and minimal stress acting on the wafer holder even if the temperature of the central part of the wafer holder is always high. Such an outcome is even more desirable.

The shape of the wafer-contacting part-of the wafer mounting surface of the wafer holder is not particularly limited as long as the shape satisfies the aforedescribed relationship between the contact surface area A in the outer circumferential area and the contact surface area B in the inner circumferential area, but one preferable shape is an annular convexity. The shape of the annular convexity is also not particularly limited, but the top part that contacts the wafer is preferably a flat surface that has, e.g., a trapezoidal or rectangular cross section. The flatness of the top part of the annular convexity is preferably 0.1 mm or less in order to ensure uniform contact with the wafer. A flatness exceeding 0.1 mm is undesirable because the relatively high portions on the annular convexity will contact the wafer locally and the temperature of the wafer will increase only at these portions, compromising the heating uniformity of the wafer.

One or a plurality of slits may be formed through the annular convexity in the widthwise direction as long as heating uniformity is not disturbed. Forming such slits results in a communication between the atmosphere on the inner and outer sides of the annular convexity adhering to the wafer, and therefore the wafer can be prevented from adhering to the wafer mounting surface or slipping out of position due to changes in air pressure within the chamber. It shall also be apparent that the width of the annular convexity is preferably uniform. If there are wider and narrow portions in the width of the annular convexity, the temperature will rise in the wider portions, disturbing the heating uniformity of the wafer. Variations in the width of the annular convexity are preferably within ±10% of the average width.

At least one annular convexity is formed on the wafer mounting surface so as to obtain the aforedescribed relationship between the contact surface areas A and B, but a plurality of annular convexities may also be formed. When forming a plurality of annular convexities, the width each of the annular convexities may be different. The individual annular convexities must satisfy the requirements for flatness and width variation described above, however.

The wafer-contacting part of the wafer mounting surface of the wafer holder may have the shape of the aforedescribed annular convexities or of “embossed” convexities. The shape of the embossed convexities is also not particularly limited. Round pillars, prismatic pillars, or a variety of other shapes may be employed. However, the shapes of embossed convexities on the same circumference of the wafer mounting surface are preferably as uniform as possible and positioned at equal intervals. These shapes and positions will allow contact between the wafer and the embossed convexities to be uniform and will allow the heating uniformity of the wafer to be maintained. The flatness of the wafer-contacting surface of the embossed convexities is preferably 0.1 mm or less. A flatness that exceeds 0.1 mm will adversely affect the temperature distribution of the wafer and is not preferable.

The wafer holder of the present invention may include a support member for supporting the wafer-holding part. The shape of the support member is not particularly limited and may be, e.g., a cylindrical pillar or a cylindrical tube. The support member may be physically anchored or chemically joined to the wafer-holding part. In order to reduce the stress acting on the wafer holder, however, anchoring the support member using, e.g., screwing or another physical method is more preferable than chemically joining the support member using brazing materials, glass, or the like.

The temperature of the support member is generally higher in the vicinity of the wafer-holding part and lower on the opposite side, and the support member is therefore prone to deformation due to this temperature difference. Chemically joining the support member to the wafer-holding part is not preferable because deformations in the support member will have an effect on the wafer-holding part, and the stress acting on the wafer-holding part will increase. When screws or other physical anchoring methods are employed, however, there is a slight amount of dimensional leeway or play between the wafer-holding part and the support member, whereas anchoring is not possible if there is no dimensional leeway. Stress occurring between the wafer-holding part and the support member is therefore largely absorbed by this leeway, making this case more preferable than chemical joining because stress is relatively minimal.

The material used for the wafer holder and the support member is not particularly limited, but aluminum, stainless steel, other metallic materials, alumina, aluminum nitride, silicon nitride, silicon carbide, other ceramic materials, or complexes of the above may be used. The selection of material may be made by taking into consideration usage temperature, cost, corrosion resistance, and other factors. Among these materials, aluminum nitride is especially preferable.

A semiconductor manufacturing apparatus provided with the wafer holder of the present invention as described above can lower the rate of breakage of the wafer holder as compared with conventional wafer holders, and therefore throughput can be improved and semiconductor productivity can be further enhanced.

A method for manufacturing the wafer holder of the present invention will be described next using a susceptor of aluminum nitride (AlN) as an example. The specific surface area of the raw AlN powder that is used is preferably 2.0 to 10.0 m²/g. The aluminum nitride sinterability will decrease if the specific surface area is less than 2.0 m²/g, and the powder will be highly likely to aggregate and difficult to use if the specific surface area exceeds 10.0 m²/g. The amount of oxygen included in the raw powder is preferably 2 wt % or less. The thermal conductivity of the sintered material will decrease if the amount, of oxygen exceeds 2 wt %. The amount of metal impurities other than aluminum that are contained in the raw powder preferably totals 2000 ppm or less. In particular, metal impurities of group-4 elements such as Si and metallic elements such as Fe act to lower thermal conductivity of the sintered material, and the content of these materials is preferably 1000 ppm or less.

AlN is a material that is resistant to sintering, and therefore a sintering agent is preferably added to the raw AlN powder. Compounds of rare-earth elements or alkaline-earth metals are preferably added as the sintering agent. These compounds react with aluminum oxides or aluminum oxynitrides on the surfaces of the aluminum nitride particles during sintering, facilitating the densification of the aluminum nitride and acting to remove the oxygen that causes a decrease in the thermal conductivity of the sintered aluminum-nitride material. The thermal conductivity of the sintered aluminum-nitride material can therefore be improved.

The amount of the sintering agent added is preferably 0.01 to 5 wt %. If the amount added is less than 0.01 wt %, a densely sintered material is difficult to obtain and the thermal conductivity of the sintered material will decrease. The sintering agent will be present in the grain boundaries of the sintered aluminum nitride if the added amount exceeds 5 wt % and will therefore be etched when corrosive atmospheres are implemented, causing grain shedding and particles. An amount of 1 wt % or less of the sintering agent is even more preferable. The sintering agent will not be present at the triple points of the grain boundaries if the amount added is 1 wt % or less, further improving the corrosion resistance of the sintered material.

Among the aforementioned sintering agents, yttrium compounds are preferable due to being particularly effective in removing oxygen. Rare-earth oxides, nitrides, fluorides, stearates or other rare-earth compounds may also be used. Among these compounds, oxides are preferable in being inexpensive and easy to acquire. Stearate compounds are ideal in having a high affinity for organic solvents, increasing miscibility when the raw AlN powder, the sintering agent, and the like are mixed in an organic solvent.

The raw AlN powder and the sintering-agent powder are mixed together after adding prescribed amounts of solvent, binders, and optional dispersants and deflocculants. The method of mixing is not particularly limited, but mixing in a ball mill, mixing using ultrasonic waves, or other methods can be used. A slurry of raw material can be obtained by mixing in this manner. The resulting slurry is shaped and sintered, whereby a sintered AlN material can be obtained. The two methods of co-firing and post-metallization can be used for sintering.

Post-metallization will be described first. A granulated powder is produced from the aforementioned slurry by spray drying or another method. The granulated powder is inserted into a prescribed metallic mold and press-molded. The force of pressing is preferably 9.8 MPa or more. When the pressure is less than 9.8 MPa, the molded material will frequently not attain adequate strength and will be easily damaged during handling and the like. The density of the molded material differs depending on the amount of binder and sintering agent added but is preferably 1.5 g/cm³ or more. The distance between particles in the raw powder will be relatively large if the density is less than 1.5 g/cm³, impeding the progress of sintering. A density of 2.5 g/cm³ or less is also preferable for the molded material. Completely removing the binder from within the molded material during the degreasing treatment of the next step will be difficult if the density exceeds 2.5 g/cm³, and therefore obtaining the compact sintered material described previously becomes difficult.

The resulting molded material is heated under a non-oxidizing atmosphere of nitrogen, argon, or the like and a degreasing treatment is performed. The surfaces of the AlN powder will be oxidized if the degreasing treatment is performed is performed under an oxidizing atmosphere of atmospheric gas or the like, reducing the thermal conductivity of the sintered material. The heating temperature during the degreasing treatment is preferably 500 to 1000° C. Completely removing the binder will not be possible and excess carbon will remain in the molded material after the degreasing treatment if the temperature is less than 500° C., hindering sintering during the subsequent sintering step. The amount of remaining carbon will be too small and the ability to remove the oxygen in the oxidized films on the surfaces of the AlN powder will decrease if the temperature exceeds 1000° C., reducing the thermal conductivity of the sintered material. The amount of carbon remaining in the molded material after the degreasing treatment is preferably 1.0 wt % or less. Sintering will be impeded and obtaining compact sintered AlN material will not be possible if the remaining carbon exceeds 1.0 wt %.

The molded material is sintered after degreasing. Sintering is carried out at a temperature of 1700 to 2000° C. under a non-oxidizing atmosphere of nitrogen, argon, or the like. The moisture content in the nitrogen gas or the like that is used preferably has a dew point of −30° C. or less. The AlN will react with the moisture in the gas during sintering to form oxynitride compounds when the moisture content has a dew point of more than −30° C., and thermal conductivity may decrease. The amount of oxygen in the gas is preferably 0.001 vol % or less. The surfaces of the AlN will be oxidized if the amount of oxygen exceeds 0.001 vol %, and thermal conductivity may decrease.

The jig used during sintering is preferably a boron nitride (BN) molded material. BN molded materials have adequate heat resistance for the aforementioned sintering temperatures and have solid-lubricating surfaces. Friction between the jig and the molded material can therefore be minimized when the molded material contracts during sintering, and the sintered AlN material will be able to be obtained with minimal warpage.

A machining process such as surface polishing is then performed on the resulting sintered AlN material as necessary. The surface roughness Ra of the sintered material is preferably 5 μm or less for the next step of screen printing an electrically conductive paste. Blurring, pinholes, and other defects are prone to occur in the pattern if the surface roughness Ra exceeds 5 μm when forming the circuit by screen printing. A surface roughness Ra of 1 μm or less is ideal. It shall be apparent that both surfaces of the sintered material should be polished to the aforedescribed surface roughness when screen printing both surfaces, but both the surface to be screen-printed and the opposite surface should be polished even when only one surface will be screen printed. When only the surface to be screen-printed is polished, the sintered material will be supported on the unpolished surface during screen printing. Protrusions and foreign substances will be present on the unpolished surface at that point, and the sintered member will therefore be unstably secured and the screen-printed circuit pattern may not be accurately drawn.

Both of the worked surfaces are preferably polished to a flatness of 0.5 mm or less. Large variations will occur in the thickness of the electrically conductive paste during screen printing if the flatness exceeds 0.5 mm. A flatness of 0.1 mm or less is ideal. The flatness of the surface to be screen printed is preferably 0.5 mm or less. Large variations will occur in the thickness of the electrically conductive paste if the flatness exceeds 0.5 mm. A flatness of 0.1 mm or less is ideal.

An electrically conductive paste is applied by screen printing to the sintered AlN material after polishing, and an electrical circuit pattern is formed. The electrically conductive paste may be obtained by mixing together a metallic powder, a binder, and a solvent. Tungsten, molybdenum, or tantalum is preferable as the metallic powder due to their having thermal expansion coefficients that are compatible with ceramics. An oxide powder may also be added to the electrically conductive paste in order to increase the strength of adhesion with the AlN. Group-3A elements, oxides of group-3A elements Al₂O₃, SiO₂, and the like are preferable as the oxide powder. Yttrium oxide is especially preferable due to having extremely good wettability with AlN. The amount of oxide powder added is preferably 0.1 to 30 wt %. The strength of adhesion between the AlN and the metal layer that forms the electrical circuit will decrease if the amount is less than 0.1 wt %, while the electrical resistance of the metal layer that forms the electrical circuit will increase if the amount exceeds 30 wt %.

The thickness of the electrically conductive paste is preferably 5 μm or more and 100 μm or less after drying. Not only does electrical resistance increase excessively when the thickness is less than 5 μm, but the strength of adhesion also decreases. The strength of adhesion also decreases when the thickness exceeds 100 μm. The spaces between the patterns on the circuit pattern that is formed are preferably 0.1 mm or more for a heater circuit (resistance-heater circuit). Electrical current will leak due to the temperature and the applied voltage when electrical current is applied to the resistance heater if the spaces are less 0.1 mm, and the danger of shorting will be increased. Pattern spacing of 1 mm or more is preferable for use at temperatures of 500° C. or more in particular, and 3 mm or more is especially preferable.

Next, the electrically conductive paste is delipidated and then fired. Degreasing is performed under a non-oxidizing atmosphere of nitrogen, argon, or the like. The degreasing temperature is preferably 500° C. or more. The binder within the electrically conductive paste will be incompletely removed and carbon will remain within the metal layer if the degreasing temperature is less than 500° C., and carbon compounds will form in the metal during firing, increasing the electrical resistance of the metal layer. The firing of the electrically conductive paste after degreasing is ideally performed at 1500° C. or more under a non-oxidizing atmosphere of nitrogen, argon, or the like. Particle growth of the metal powder within the electrically conductive paste will not progress if the temperature is less than 1500° C., excessively increasing the electrical resistance of the post-firing metal layer. Additionally, the firing temperature should not exceed the sintering temperature of the ceramic. The sintering agents and the like contained in the ceramic will begin to sublimate and the particles of metallic powder in the electrically conductive paste will be spurred to further growth if the electrically conductive paste is fired at a temperature that exceeds the sintering temperature of the ceramic, and the strength of adhesion between the ceramic and the metal layer will decrease.

An insulating coat may then be formed on the metal layer that forms the electrical circuit in order to ensure the insulation of the metal layer. The material of the insulating coat is not particularly limited as long as the material is minimally reactive with the metal layer and the difference between the thermal expansion coefficients of AlN and the material is 5.0×10⁻⁶/K or less. Crystallized glass, AlN, and the like may be used, for example. The material is formed into, e.g., a paste and screen printed at a prescribed thickness. Degreasing is performed as necessary, and the material is then fired at a prescribed temperature, allowing the insulating coat to be formed.

The amount of sintering agent added to the paste at this point is preferably 0.01 wt % or more. The insulating coat will not be compacted if the amount of the sintering agent is less than 0.01 wt %, and the metal layer will tend not to be reliably insulated. The amount of the sintering agent preferably does not exceed 20 wt %. An excess of the sintering agent will permeate the metal layer if the amount of the sintering agent exceeds 20 wt %, and the electrical resistance of the metal layer may change. The thickness of the applied paste is not particularly limited but is preferably 5 μm or more. Maintaining insulation will be difficult if the thickness is less than 5 μm.

Compounds and alloys of silver, palladium, platinum, and the like can be used as the aforedescribed electrically conductive paste. By adding palladium or platinum in proportion to the silver content, these metals will increase the volume resistivity of a conductor, and therefore the amount added may be adjusted in accordance with the circuit pattern. These additives also have the effect of preventing migration between circuit patterns, and therefore 0.1 or more parts by weight of additive per 100 parts by weight of silver is preferable.

A metal oxide is preferably added to this metal powder in order to ensure adhesion with AlN. For example, aluminum oxide, silicon oxide, copper oxide, boron oxide, zinc oxide, lead oxide, oxides of rare-earth elements, oxides of transition metals, oxides of alkaline-earth metals, and the like may be added. The amount added is preferably 0.1 wt % or more and 50 wt % or less. A metal oxide content of less than 0.1 wt % is not preferable because adhesion with aluminum nitride will decrease. A metal oxide content of more than 50 wt % is not preferable because sintering of the silver and other metal components will be impeded. The metal powder and the metal-oxide powder are mixed, an organic solvent and a binder are also added, and a paste is formed. The circuit pattern is then formed using screen printing as described above. The circuit pattern formed in this instance is fired at 700° C. to 1000° C. under atmospheric gas or under an inert gas atmosphere of nitrogen or the like.

Crystallized glass, glazed glass, an organic resin, or the like is then applied and fired or cured in this case, whereby an insulation layer can be formed to ensure insulation between the circuits. The type of glass used may be boron silicate glass, lead oxide, zinc oxide, aluminum oxide, silicon oxide, or the like. An organic solvent and a binder are added to the glass powder, and a paste is formed that is applied by screen printing. The thickness with which the paste is applied is not particularly limited, but 5 μm or more is preferable. Insulation will be difficult to maintain if the thickness is less than 5 μm. The firing temperature is preferably lower than the temperature during circuit formation described above. Firing at a temperature higher than the temperature during the aforedescribed circuit formation is not preferable because significant changes will occur in the resistance of the circuit pattern.

A ceramic substrate layer may also be added subsequently, as necessary. Layering should be performed using a bonding agent. The bonding agent may be formed by adding a binder, a solvent, and a compound of a group-2A elements or group-3A element to an aluminum oxide powder or aluminum nitride powder, forming a paste that is applied to the joining surface using screen printing or another method. The thickness of the applied bonding agent is not particularly limited but is preferably 5 μm or more. Pinholes, irregularities, and other joining defects are prone to occur in the joining layer if the thickness is less than 5 μm.

The ceramic substrate on which the bonding agent has been applied is delipidated at a temperature of 500° C. or more under a non-oxidizing atmosphere. The ceramic substrates to be layered are then overlaid, a prescribed load is applied, and heating is performed under a non-oxidizing atmosphere, whereby the ceramic substrates are joined together. The load is preferably 5 kPa or more. Adequate joining force may be unobtainable or joining defects may occur if the load is less than 5 kPa. As long as the temperature facilitates adequate adhesion of the ceramic substrates via the joining layer, the temperature during joining is not particularly limited but is preferably 1500° C. or more. Adequate joining strength will be difficult to obtain and joining defects will readily occur if the temperature is less than 1500° C. The non-oxidizing atmosphere used during degreasing and joining preferably employs nitrogen, argon, or the like.

A ceramic-layered sintered material that acts as the wafer-holding part of the wafer holder can be obtained as above. If the electrical circuit is a heater circuit, a mesh (net) of molybdenum or tungsten may also be used instead of an electrically conductive paste when using, e.g., molybdenum wires (coils), electrodes for electrostatic adsorption, RF electrodes, and the like.

The molybdenum coils and mesh in such instances are embedded within the raw AlN powder and can be produced by hot-press methods. The temperature and atmosphere used for the AlN sintering may be applied as the temperature and atmosphere of hot pressing, but the force of the hot press is preferably 1.0 MPa or more. Gaps will occur between the AlN and the molybdenum coils and mesh if the hot-press force is less than 1.0 MPa, and heater functionality may not occur.

The co-firing method will be described next. The previously described raw slurry is molded into a sheet using a doctor-blade method. The molding of the sheet is not particularly limited, but the thickness of the sheet is preferably 3 mm or less after drying. The slurry will contract significantly during drying if the thickness of the sheet exceeds 3 mm, increasing the probability of cracks appearing in the sheet. An electrically conductive paste is applied to the resulting sheet using screen printing or another method, whereby a metal layer is formed into a prescribed shape that will act as the electrical circuit pattern. The same materials described in the post-metallization method may be used in the electrically conductive paste. In the co-firing method, however, no harm will result if an oxide powder is not added to the electrically conductive paste.

The sheet upon which the aforedescribed circuit pattern was formed is layered together with a sheet upon which no circuit has been formed. The method of layering involves setting and overlaying the sheets in prescribed positions. A solvent is applied between the sheets at this point as necessary. The overlaid sheets are then heated as necessary. The heating temperature is preferably 150° C. or less. Large deformations will occur in the layered sheets if the sheets are heated at a temperature that exceeds 150° C. Pressure is then applied to integrate the overlaid sheets. The pressure applied is preferably 1 to 100 MPa. The sheets will not be fully integrated if the pressure is less than 1 MPa and may separate during subsequent steps. Unacceptably large deformations will occur in the sheets if the pressure exceeds 100 MPa.

Degreasing and sintering are performed on the layered material as in the aforedescribed post-metallization method. The temperature, carbon content, and other conditions during degreasing and sintering are the same as in the post-metallization method. Heater circuits, electrodes for electrostatic adsorption, and the like are printed on a plurality of sheets when printing the aforedescribed electrically conductive paste on the sheets, which are then layered, allowing an electric heater that has a plurality of electrical circuits to be easily manufactured. A ceramic-layered sintered material that acts as the wafer-holding part of the wafer holder can thus be obtained.

When the electrical circuits for the heater circuit and the like are formed on the outermost layer of the ceramic-layered material, an insulating coat may be formed on the electrical circuit as in the aforedescribed post-metallization method in order to protect the electrical circuit and ensure insulation. The resulting ceramic-layered sintered material is then processed as necessary, because in a sintered state the material often lacks the precision necessary for the semiconductor manufacturing apparatus. The precision with which the working is performed is preferably 0.1 mm or less in terms of the flatness of the wafer mounting surface at the wafer-contacting part of the annular convexities or embossments. Gaps are prone to appear between the wafer holder and the wafer to be processed if the flatness exceeds 0.1 mm, and the heat of the wafer holder will not be uniformly conveyed to the material to be processed. Temperature variation will therefore be prone to occur in the material to be processed.

The surface roughness Ra of the wafer mounting surface is preferably 5 μm or less. AlN particle shedding due to friction between the wafer holder and the wafer will be frequent if the surface roughness Ra exceeds 5 μm. These shed particles exert a negative effect on film formation, etching, and other treatments performed on the wafer. A surface roughness Ra of 1 μm or less is particularly preferable. A susceptor wafer-holding part that acts as the wafer holder can be produced as described above.

A support member is attached to the wafer-holding part of the resulting wafer holder. The attachment of the support member may involve chemical joining using a joining layer or attachment using physical (mechanical) methods such as screwing and the like. The material of the support member is not particularly limited as long as the material has a thermal expansion coefficient that is not significantly different from the thermal expansion coefficient of the ceramic of the wafer-holding part, but the difference in thermal expansion coefficients between the wafer-holding part and the material is preferably 5×10⁻⁶/K or less. Cracks and the like readily appear in the vicinity of the attachment point between the wafer-holding part and the support member during joining when the difference in thermal expansion coefficients exceeds 5×10⁻⁶/K, especially in the case of chemical joining. Even if cracks do not appear during joining, the joining site will be subjected to a heat cycle after repeated uses, and breaking and cracking may occur. The material of the support member is ideally AlN when the wafer-holding part is AlN, but, e.g., silicon nitride, silicon carbide, mullite, or the like may also be used.

The joining layer when chemical joining is performed preferably comprises AlN, Al₂O₃, and an oxide of a rare-earth element. These components are preferable due to having good wettability with the AlN or other ceramic material of the wafer-holding part and the support member, and therefore the strength of joining is relatively high and an airtight joining surface is easily obtained. The flatness of the joining surfaces of the support member and the wafer-holding part to be joined is preferably 0.5 mm or less. Gaps readily form between the joining surfaces if the flatness exceeds 0.5 mm, hindering adequately airtight joining. A flatness of 0.1 mm or less is ideal. The flatness of the joining surface of the wafer-holding part is ideally 0.02 mm or less. The surface roughness Ra of the joining surfaces is preferably 5 μm or less. Gaps will readily form between the joining surfaces when the surface roughness Ra exceeds 5 μm. A surface roughness Ra of 1 μm or less for the joining surfaces is ideal.

The support member may also be attached by screwing or other physical (mechanical) methods. When the support member is, e.g., tube-shaped, a flange part is formed on the inside or the outside of the support member. Through-holes or screw holes are formed in a plurality of locations (three or more locations, if possible), and screw holes are also formed in the wafer-holding part. Male screws are screwed into these holes, allowing the support member to be attached to the wafer-holding part. These male screws are formed from a material that has a thermal expansion coefficient that is relatively close to the thermal expansion coefficients of the wafer-holding part and the support member, The outside or the inside of the support member may be anchored as necessary using this attachment method, but anchoring the inside of the support member is preferable in order to minimize stress acting on the wafer-holding part.

Electrodes are then attached to the wafer-holding part. The electrodes may be attached using a well-known method. For example, a countersinking may be formed in the surface opposite the wafer mounting surface of the wafer-holding part to the electrical circuit, and electrodes of molybdenum, tungsten, or the like may be connected using direct active-metal brazing with or without metallizing the electrical circuit. The electrodes may then be plated as necessary in order to improve oxidation resistance.

Finally, an annular groove is mechanically formed in and around the vicinity of the joining site between the wafer-holding part and the support member when the wafer-holding part and the support member have been joined by chemical methods. A wafer holder (susceptor) for a semiconductor manufacturing apparatus can thus be produced. The annular groove may also be formed beforehand on the unsintered molded material or may be formed before the support member is joined.

Semiconductor wafers can be processed by incorporating the wafer holder of the present invention into a semiconductor manufacturing apparatus. The attachment point between the wafer-holding part and the support member of the wafer holder of the present invention is highly reliable, allowing semiconductor wafers to be stably processed for long periods of time.

WORKING EXAMPLES

0.5 parts by weight of yttrium oxide was added as a sintering agent to 99.5 wt % aluminum nitride powder. A binder and an organic solvent were also added. Mixing was performed in a ball mill to produce a slurry. The resulting slurry was spray-dried to produce a granulated powder, which was molded to produce molded materials. After degreasing the molded materials under a temperature of 700° C. in a nitrogen atmosphere, the molded materials were sintered at 1850° C. in a nitrogen atmosphere to obtain sintered aluminum-nitride materials. The resulting sintered materials were machined to a diameter of 330 mm and a thickness of 10 mm. The surface thickness Ra was 0.8 μm and the flatness was 50 μm.

A W paste was applied by screen printing to the sintered aluminum-nitride materials. After degreasing at 700° C. in a nitrogen atmosphere, firing was performed at 1830° C. in a nitrogen atmosphere, whereby resistance heaters were formed. The resulting resistance heaters were fashioned as two-zone heaters capable of separately controlling temperature on the inner circumferential part and the outer circumferential part of the wafer mounting surface. An aluminum-nitride paste containing yttrium oxide was also applied by screen printing to the resistance heaters, delipidated at 700° C., and then fired at 1820° C. AlN powder, Al₂O₃ powder, and Y₂O₃ powder were then mixed together and a binder and an organic solvent were added to form a bonding agent paste. The bonding agent paste was applied to the surface of the aforedescribed sintered aluminum-nitride materials to which the aluminum-nitride paste has been applied and delipidated at 700° C. in a nitrogen atmosphere.

Aluminum-nitride substrates that were machined to a diameter of 330 mm and a thickness of 10 mm were also prepared. These aluminum-nitride substrates were mounted on the surfaces of the sintered aluminum-nitride materials to which the bonding agent paste was applied. A load of 10 tons was applied by hot pressing, and joining was carried out at 1800° C. One surface of the resulting joined materials was made into the wafer mounting surface, and the opposite surface was counter-sunk up to the resistance heater. Tungsten electrodes were attached by silver brazing. A flange part was provided to one end of aluminum-nitride support members (outside diameter 80 mm, inside diameter 70 mm) so as to cover the electrodes and was anchored in four locations by screws of aluminum nitride, completing the wafer holders.

The wafer mounting surfaces of the resulting wafer holders were machined to form the wafer-contacting parts. The annular convexities of the various shapes designated by a through k in Table 1 below were used as the shapes of the wafer-contacting part. By combining one or a plurality of the annular convexities of Table 1, wafer mounting surfaces were formed having wafer-contacting parts in the inner circumferential area and the outer circumferential area as shown for each sample in Table 2.

The ring location in Table 1 is the distance from the center of the wafer mounting surface to the center of the annular convexity indicated. In Table 2, both the contact surface area B in the inner circumferential area and the contact surface area A in the outer circumferential area are indicated for the contact surface area between the wafer mounting surface and the wafer.

Heating uniformity under heating at 800° C. was measured for the wafer holders of each sample shown in Table 2, and heat-cycle tests were performed up to 800° C. The temperature of the wafers was measured using a wafer thermometer having a diameter of 300 mm, and the temperature of the wafers was raised while controlling the temperature to ±1%. The results are shown in Table 2. TABLE 1 Annular Ring location Ring width Ring area Convexity (mm) (mm) (cm²) a 10 1 0.6 b 50 1 3 c 50 2 6 d 75 1 5 e 75 2 9 f 100 1 6 g 100 2 13 h 130 1 8 i 130 2 16 j 145 1 9 k 145 2 18

TABLE 2 Shape of wafer mounting Inner Outer surface circumferential circumferential Inner Outer contact surface contact surface Heating Sample side side area B (cm²) area A (cm²) uniformity (%) 1 Flat Flat 353 353 Broken at 700° C. 2 c e g h k 28 26 Broken at 680° C. 3 e g h k 22 26 ±1.2 4 g h k 13 26 ±0.9 5 f h k 6 26 ±0.8 6 a h k 0.6 26 ±0.6 7 Flat h 0 8 ±0.5 8 Flat i 0 16 ±0.5 9 Flat j 0 9 ±0.4 10 Flat k 0 18 ±0.4 

1. A wafer holder for a semiconductor manufacturing apparatus including a resistance heater, the wafer holder comprising: a wafer holding part having a wafer mounting surface configured and arranged to support a wafer such that a surface area of contact between the wafer and the wafer mounting surface satisfies the relation A>B, where A is a contact surface area in an outer circumferential area that is farther than 1/√2R from a center of the wafer, R is the radius of the wafer, and B is a contact surface area in an inner circumferential area that is within 1/√2R of the center of the wafer.
 2. The wafer holder for a semiconductor manufacturing apparatus according to claim 1, wherein the contact surface area between the wafer and the wafer mounting surface is established so that A>2B.
 3. The wafer holder for a semiconductor manufacturing apparatus according to claim 1, wherein the contact surface area between the wafer and the wafer mounting surface is established so that B=0.
 4. The wafer holder for a semiconductor manufacturing apparatus according to claim 1, wherein the wafer mounting surface has a wafer-contacting part that is shaped as an annular convexity.
 5. The wafer holder for a semiconductor manufacturing apparatus according to claim 1, wherein the wafer mounting surface has a wafer-contacting part that is shaped as an embossed convexity.
 6. The wafer holder for a semiconductor manufacturing apparatus according to claim 1, further comprising a support member configured and arranged to support the wafer-holding part, wherein the support member is physically anchored or chemically joined to the wafer-holding part.
 7. A semiconductor manufacturing apparatus comprising the wafer holder of claim
 1. 